While trapmasters are a cool idea and add some variability to the game. They also add a couple things I see as issues that can't be avoided. All of these pertain to hallways.

First of all, it is known that mist elves just die to traps early. This increases the frequency of this and makes them even harder to get started with.

Next, with the addition of the Tome of Donors, it already has significantly decreased the desirability of precrowning. I've noticed that a single trap master can almost completely shut down an early precrown with 1 pit or acid trap in the wrong place, further decreasing the desirability of precrowns.

Lastly, the puppy. It's already relatively tough to save the puppy early (while waiting is always an option, this means no access to the early lesser vault). Now one trap from a trap master can completely shut down any chance to save it.

My suggestion: Increase the trap masters stats (PV, damage, health) but also increase their danger level maybe to 6 or 7 so they do not spawn quite as early. This would still let them be a fun new monster while not completely shutting down a lot of early game tactics which already aren't seen often.